U.S. patent number 8,575,547 [Application Number 12/982,202] was granted by the patent office on 2013-11-05 for electron beam measurement apparatus.
This patent grant is currently assigned to Hitachi High-Technologies Corporation. The grantee listed for this patent is Muneyuki Fukuda, Shoji Hotta, Shinji Okazaki, Yasunari Sohda. Invention is credited to Muneyuki Fukuda, Shoji Hotta, Shinji Okazaki, Yasunari Sohda.
United States Patent |
8,575,547 |
Sohda , et al. |
November 5, 2013 |
Electron beam measurement apparatus
Abstract
The present invention provides an electron beam measurement
technique for measuring the shapes or sizes of portions of patterns
on a sample, or detecting a defect or the like. An electron beam
measurement apparatus has a unit for irradiating the patterns
delineated on a substrate by a multi-exposure method, and
classifying the patterns in an acquired image into multiple groups
according to an exposure history record. The exposure history
record is obtained based on brightness of the patterns and a
difference between white bands of the patterns.
Inventors: |
Sohda; Yasunari (Kawasaki,
JP), Hotta; Shoji (Delmar, NY), Okazaki;
Shinji (Saitama, JP), Fukuda; Muneyuki
(Kokubunji, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sohda; Yasunari
Hotta; Shoji
Okazaki; Shinji
Fukuda; Muneyuki |
Kawasaki
Delmar
Saitama
Kokubunji |
N/A
NY
N/A
N/A |
JP
US
JP
JP |
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Assignee: |
Hitachi High-Technologies
Corporation (Tokyo, JP)
|
Family
ID: |
40720640 |
Appl.
No.: |
12/982,202 |
Filed: |
December 30, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110095183 A1 |
Apr 28, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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12328161 |
Dec 4, 2008 |
7884325 |
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Foreign Application Priority Data
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Dec 6, 2007 [JP] |
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2007-315940 |
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Current U.S.
Class: |
250/306; 250/311;
250/309; 250/307; 250/310; 356/394 |
Current CPC
Class: |
G03F
7/70541 (20130101); G03F 7/7065 (20130101); G03F
7/70625 (20130101); G06T 7/0006 (20130101); G06T
2207/30148 (20130101); H01J 2237/2817 (20130101); G06T
2207/10056 (20130101); H01J 2237/24578 (20130101); H01J
2237/221 (20130101); H01L 22/12 (20130101) |
Current International
Class: |
G01N
23/00 (20060101); G21K 7/00 (20060101) |
Field of
Search: |
;250/306,307,309-311,397
;356/394 ;850/9,10 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
Semiconductor International Web-version
http://www.sijapan.com/issue/2007/04/u3eqp3000001dd9m.html. cited
by applicant.
|
Primary Examiner: Berman; Jack
Assistant Examiner: Sahu; Meenakshi
Attorney, Agent or Firm: Mattingly & Malur, PC
Parent Case Text
This is a continuation application of U.S. application Ser. No.
12/328,161, filed Dec. 4, 2008, now allowed, the contents of which
are hereby incorporated by reference into this application.
Claims
What is claimed is:
1. An electron beam measurement apparatus, which measures, based on
information on an image, patterns formed on a sample, comprising:
an electron optical system that has a lens and a deflector and
scans a predetermined observation region on the sample with an
electron beam emitted from an electron source, a detector for
detecting a charged particle secondarily generated from the sample
by irradiation with the electron beam, and a means for forming an
image including forming a secondary electron image using a
secondary electron and a reflective electron image using a
reflective electron based on the detected charged particle, wherein
the patterns are delineated in a single layer present on a
substrate, and further including a means for classifying patterns,
which are arranged in an image acquired by the irradiation with the
electron beam irradiated on the patterns on the sample, into at
least one of first and second groups based on the secondary
electron image and the reflective electron image.
2. The electron beam measurement apparatus according to claim 1,
wherein an image processing parameter or a waveform processing
parameter is used for each of the groups to obtain the size of a
portion of the pattern included in the group or a position of the
contour of the portion of the pattern, wherein the parameter used
varies depending on the group.
Description
CLAIM OF PRIORITY
The present application claims priority from Japanese patent
application JP 2007-315940, filed on Dec. 6, 2007, the content of
which is hereby incorporated by reference into this
application.
BACKGROUND OF THE INVENTION
The present invention relates to an electron beam measurement
technique for measuring the shapes or sizes of portions of patterns
on a sample, or detecting a defect or the like.
In recent years, a semiconductor element has been miniaturized, and
dimensional control with high accuracy has been demanded. With the
miniaturization of the semiconductor element, the wavelength of
light used in a lithographic process has been reduced. In the most
currently advanced factory, an ArF excimer laser (having a
wavelength of 193 nm) is used. In order to miniaturize the
semiconductor element, an extreme ultraviolet (EUV) lithography
using light with a wavelength of 13 nm is considered as a
candidate. However, since the wavelength of light used in the EUV
lithography is shorter by one digit or more than that of the ArF
excimer laser, there is a controversy whether or not it is possible
to smoothly switch to the EUV lithography. As an alternative
solution, a multi-exposure scheme has been proposed.
As an example of the multi-exposure scheme, a process flow of a
double patterning technique (refer to, for example, SEMICONDUCTOR
International Web-version:
http://www.sijapan.com/issue/2007/04/u3eqp3000001dd9m.html) is
shown in FIGS. 1A to 1G. As shown in FIG. 1A, a substrate W has a
processed layer TL, a hard mask layer HM and a first resist layer
RL1. The hard mask layer HM is provided on the processed layer TL.
The first resist layer RL1 is provided on the hard mask layer
HM.
In a first exposure, a first exposure pattern EP1 is delineated in
the first resist layer RL1 by an exposure apparatus (as shown FIG.
1B) and developed (as shown in FIG. 1C). Next, the hard mask layer
HM is etched such that the first pattern is transferred into the
hard mask layer HM as shown in FIG. 1D.
Then, an antireflection film BARC is formed in order to perform a
second exposure. After that, a second resist layer RL2 is formed
(as shown in FIG. 1E). The second exposure is performed by using an
appropriate reticle in the same way as the first exposure such that
a second exposure pattern EP2 is delineated in the second resist
layer RL2 (as shown in FIG. 1E) and developed (as shown in FIG.
1F). A portion of the second exposure pattern EP2 is located
between portions of the first exposure pattern EP1. This makes it
possible to delineate a fine pattern (that cannot be delineated by
a single exposure due to a lack of resolution) in a single
layer.
Next, the processed layer TL is etched using the second resist
layer RL2, the antireflection film BARC, and the hard mask layer HM
as masks. Then, the second resist layer RL 2 and the antireflection
film BARC are peeled off. A pattern of the processed layer TL is
formed as shown in FIG. 1G. In this case, the hard mask layer HM is
typically not removed. The wafer is inspected in this state (shown
in FIG. 1G).
SUMMARY OF THE INVENTION
Conventionally, only a sample subjected to a single exposure is
targeted in the case where an electron beam measurement apparatus
measures the sizes of portions of patterns on the sample. That is,
it has been unclear how to measure a sample subjected to a
multi-exposure scheme and having a pattern that includes portions
having shapes different from each other in a vertical
direction.
It is, therefore, an object of the present invention to provide a
technique which uses an electron beam to measure a sample
manufactured by a multi-exposure scheme.
To accomplish the object, it is effective to provide means for
classifying patterns in an image acquired by charged beam scanning
into multiple groups according to an exposure history record, based
on brightness of the patterns and a difference between white bands
of the patterns. In addition, it is preferable to provide means
which uses an image processing parameter or a waveform processing
parameter for each of the groups, and measuring the size of a
portion of a pattern, the position of the contour of the pattern,
or a relative positional relationship be conducted. In this case,
the used parameter varies depending on the group.
As the means for classifying the patterns into groups, it is
effective to provide means for comparing an acquired image with a
design database. As the means for measuring the size of a portion
of a pattern or the position of the contour of the pattern, a
reference image or a reference waveform may be used. It is also
effective to provide means which uses conditions for image
acquisition itself to acquire images that have the same pattern and
are different from each other, and processes the images.
Representative configuration examples of the present invention are
described below.
(1) An electron beam measurement apparatus, which measures, based
on information on an image, a pattern formed on a sample,
comprising: an electron optical system that uses a lens and a
deflector to scan a predetermined observation region on a sample
with an electron beam emitted from an electron source; a detector
for detecting a charged particle secondarily generated from the
sample by irradiation with the electron beam; and means for forming
an image based on the detected charged particle. The electron beam
measurement apparatus includes means for classifying patterns,
which are included in an image acquired by the irradiation with the
electron beam on the patterns on the sample, into groups according
to an exposure history record. The exposure history record is
obtained based on brightness of the patterns included in the image
and a difference between shapes of white bands of the patterns. The
patterns are delineated in a single layer present on a substrate by
a multi-exposure method. Image processing or waveform processing is
preformed on each group, the processing varying depending on the
classified group.
(2) The electron beam measurement apparatus having the
configuration described in item (1), wherein the patterns are
classified into the groups based on an image formed based on a
secondary electron of the charged particle and an image formed
based on a reflective electron of the charged particle.
(3) The electron beam measurement apparatus having the
configuration described in item (1), wherein the patterns are
classified into the groups according to the exposure history record
by comparing the acquired image with a design database.
(4) The electron beam measurement apparatus having the
configuration described in item (1), wherein the patterns are
classified into the groups such that a pattern having portion
arranged alternately is included in one of the groups that is
different from the other group including the other pattern.
(5) The electron beam measurement apparatus having the
configuration described in item (1), wherein an image processing
parameter or an waveform processing parameter is used for each of
the classified groups to obtain the size of a portion of the
pattern included in the group or the position of the contour of the
portion of the pattern, the used parameter varying depending on the
group.
(6) The electron beam measurement apparatus having the
configuration described in item (1), wherein a reference image or a
reference waveform is used for each of the classified groups to
obtain the size of a portion of the pattern included in the group
or the position of the contour of the portion of the pattern, the
used reference image or the used reference waveform varying
depending on the group.
(7) The electron beam measurement apparatus having the
configuration described in item (1), wherein information on a
relative positional relationship between the classified groups is
obtained.
(8) An electron beam measurement apparatus, which measures, based
on information on an image, a pattern formed on a sample,
comprising: an electron optical system that uses a lens and a
deflector to scan a predetermined observation region on a sample
with an electron beam emitted from an electron source; a detector
for detecting a charged particle secondarily generated from the
sample by irradiation with the electron beam; and means for forming
an image based on the detected charged particle, the patterns being
delineated in a single layer present on a substrate by a
multi-exposure method. The electron beam measurement apparatus
including means for classifying the patterns in the plurality of
images into a plurality of groups according to an exposure history
record by irradiating patterns present on the sample with the
electron beam to acquire a plurality of images respectively
indicating regions that mostly overlap each other under respective
conditions different from each other.
(9) The electron beam measurement apparatus having the
configuration described in item (8), wherein the multi-exposure
method uses a double patterning technique.
(10) The electron beam measurement apparatus having the
configuration described in item (8), wherein the image formed based
on the detected charged particle is a scanning electron microscope
image.
According to the present invention, it is possible to realize an
electron beam measurement technique capable of measuring the shape
or size of a portion of a pattern delineated on a sample by a
multi-exposure method or detecting a defect or the like.
BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A to 1G are diagrams showing an example of a process flow of
a multi-exposure method.
FIG. 2 is a diagram showing a basic configuration of an electron
beam measurement apparatus according to the present invention.
FIG. 3 is a flowchart showing a basic measurement according to the
present invention.
FIG. 4 is a flowchart showing a measurement according to a first
embodiment of the present invention.
FIG. 5 is a flowchart showing a measurement according to a second
embodiment of the present invention.
FIG. 6 is a flowchart showing a measurement according to a third
embodiment of the present invention.
FIG. 7 is a flowchart showing a measurement according to a fourth
embodiment of the present invention.
FIG. 8 is a flowchart showing a measurement according to a fifth
embodiment of the present invention.
FIG. 9 is a diagram showing an example of a scanning electron
microscope (SEM) image.
FIG. 10A is a diagram showing a secondary electron image.
FIG. 10B is a diagram showing a reflective electron image.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiments of the present invention will be described with
reference to the accompanying drawings.
(First Embodiment)
First, a basic configuration of an electron beam measurement
apparatus according to the present invention will be described.
FIG. 2 is a diagram showing the basic configuration of the electron
beam measurement apparatus according to the present invention. The
electron beam measurement apparatus has an electron optical system
201, a secondary electron detector 208, a reflective electron
detector 215, a computing unit 209, a display unit 210, a storage
unit 211, and an electron optical system controller 212. The
electron optical system 201 uses a condenser lens 203, a deflector
204 and an objective lens 205 to irradiate a sample (wafer) 207
placed on a stage 206 with an electron beam emitted by an electron
gun 202 and scan the sample. The secondary electron detector 208 is
adapted to detect the intensity of a charged particle (secondary
electron) secondarily generated from the sample 207 by the
irradiation of the electron beam. The reflective electron detector
215 is adapted to detect the intensity of a charged particle
(reflective electron) secondarily generated from the sample 207 by
the irradiation of the electron beam. The computing unit 209 is
adapted to process the waveform of a signal obtained from the
detected charged particle to calculate a characteristic value. The
display unit 210 displays, through an input performed by an
operator, a scanning electron microscope (SEM) image. The storage
unit 211 stores data. The electron optical system controller 212
reflects a condition for the irradiation with the electron beam to
the electron optical system to control the electron optical
system.
It should be noted that reference numeral 213 shown in FIG. 2
denotes flow of data (e.g., flow of a computed result) to be stored
in the storage unit 211, and reference numeral 214 shown in FIG. 2
denotes flow of data read out from the storage unit 211.
FIG. 3 is a flowchart showing a basic measurement according to the
present invention. First, coordinates of an area to be measured are
acquired in step 301. The scanning electron microscope (SEM) image
of the region located at the coordinates is acquired by means of a
secondary electron in step 302. Data on the acquired image is
stored in the storage unit 211 in step 303. Patterns within the
acquired image are classified into two groups (group 1 and group 2)
in accordance with a predetermined rule in step 303. The size of a
portion of a pattern of each group is calculated in accordance with
a predetermined algorithm in steps 305 and 306.
It can be determined whether or not each exposure process is
properly performed by determining whether or not each calculated
size is in a predetermined range. If there is a group including a
pattern having a portion of which the size is not in a
predetermined range, a process condition for a corresponding
exposure process is reviewed. In the abovementioned way, it is
possible to control processes of a multi-exposure method according
to the present invention.
The present embodiment will be described with reference to FIG.
4.
In the present embodiment, an SEM image of the sample in the state
shown in FIG. 1G is acquired. FIG. 9 is a schematic diagram showing
the SEM image. A pattern shown in FIG. 9 is part of a flash memory
pattern. A portion of the pattern shown in FIG. 9, which
corresponds to a portion (at which the hard mask layer HM remains
after a first exposure) of the sample, has higher contrast with the
substrate than that of a portion of the pattern shown in FIG. 9,
which corresponds to a portion (at which the hard mask layer HM
does not remain and the processed layer remains after a second
exposure) of the sample.
As an example of the classification method shown in FIG. 3, it is
possible to classify patterns into two patterns: a pattern
delineated by the first exposure; and a pattern delineated by the
second exposure, in accordance with brightness of the patterns (in
step 401). When the pattern includes a defect, it is possible to
easily determine which exposure process has a problem.
In addition, the algorithm for calculating the size of a portion of
the pattern can be changed to another algorithm for calculating the
size of the portion. An SEM image of a certain portion (of the
pattern) is viewed differently from an SEM image of another portion
(of the pattern) having a height different from that of the certain
portion and having other dimensions that are the same as those of
the certain portion. It is therefore necessary to change the
algorithm based on the portion of the pattern in order to optimally
measure the portion. In the present embodiment, the size of the
portion of the pattern is calculated based on coordinates of an
intersection of a signal waveform and a slice level. A slice level
for the hard mask layer HM is high, while a slice level for the
processed layer TL is low. It is possible to set a plurality of
slice levels in the electron beam measurement apparatus according
to the present embodiment.
In the present embodiment, dimensional control is carried out by
using the average of widths of a plurality of lines formed in each
layer as the size of a portion of the pattern. However, the
dimensional control may be carried out by using the width of one
line located at a central portion of each layer.
In order to classify patterns into groups, it is effective to use a
difference between white bands. The white bands are waveforms of
signals coming from edge portions of the patterns when an SEM
performs irradiation with an electron beam. In addition, reference
waveforms may be used to calculate the sizes of pattern
portions.
In a conventional technique, a measurement error between a first
exposure layer and a second exposure layer is 3 nm. According to
the present invention, however, a measurement error between exposed
layers is 0.2 nm. In addition, although a reproducible error in the
conventional technique is 0.6 nm, a reproducible error in the
present invention is 0.3 nm.
(Second Embodiment)
FIG. 5 is a flowchart of the measurement according to a second
embodiment of the present invention. In the measurement shown in
FIG. 5, after an SEM image is acquired, patterns are classified
into groups by comparing the SEM image with design data, in step
501. In the pattern (shown in FIG. 9) having lines and spaces which
are alternately arranged, matching of the pattern may be performed
with a single pitch shifted. This measurement method shown in FIG.
5 is suitable for a logic LSI having a complex pattern. It can be
considered that a combination of this measurement method shown in
FIG. 5 with the classification method based on the brightness in
the first embodiment is effective.
According to the present embodiment, the contour of a portion of
each pattern is detected, and the length of the contour is
evaluated, to inspect a hot spot (which is a location at which a
defect is likely to occur). As a result, detection sensitivity can
be improved in the present embodiment, compared with the
conventional technique.
(Third Embodiment)
FIG. 6 is a flowchart showing a measurement according to a third
embodiment of the present invention. In the present embodiment, a
plurality of images is used. After the sample is moved to a
location defined by coordinates of an area to be imaged, a single
SEM image is acquired under a first condition in step 601, and a
single SEM image is acquired in step 602 under a second condition
different from the first condition. Under the first condition, the
number of times of scanning of an observation area is eight. Under
the second condition, the number of times of television scanning of
the observation area is 32. The reason for acquiring the images
under the conditions different from each other is that the
intensity of a signal coming from the processed layer is low. Thus,
the number of times of the scanning under the second condition is
32 in order to improve a signal-to-noise ratio. The intensity of a
signal coming from the hard mask layer is too high when the image
acquisition is performed under the second condition. Thus, a
detected signal is saturated.
After the patterns are classified, the size of the hard mask layer
is obtained based on the image acquired under the first condition,
and the size of the processed layer is obtained based on the image
acquired under the second condition. As a result, a reproducible
error is reduced to 0.25 nm.
(Fourth Embodiment)
FIG. 7 is a flowchart showing a measurement according to a fourth
embodiment of the present invention. In the fourth embodiment, a
plurality of images is used. The sample shown in FIG. 1F is used
only in the fourth embodiment. After the sample is moved to a
location defined by acquired coordinates of an area to be measured,
a single SEM image is acquired by using a secondary electron in
step 701 and a single SEM image is acquired by using a reflective
electron in step 702. The second resist layer RL 2 shown in FIG. 1F
can be easily observed. It is not easy to observe the hard mask
layer HM since the hard mask layer HM is covered with the
antireflection film BARC.
In order to observe the hard mask layer HM, a reflective electron
is used. This results from the fact that the escape depth (to allow
the reflective electron to escape from the sample) of the
reflective electron is large. FIGS. 10A and 10B are diagrams
showing the image (secondary electron image) acquired by using the
secondary electron and the image (reflective electron image)
acquired by using the reflective electron image, respectively. In
the secondary electron image shown in FIG. 10A, an image of the
second resist layer RL2 is observed. In the reflective electron
image shown in FIG. 10B, an image of the second resist layer RL2
and an image of the hard mask layer HM are observed. In this
method, the two images can be acquired simultaneously. The
throughput of the electron beam measurement apparatus is therefore
not reduced. In addition, it is easy to classify the patterns into
groups based on the two images. The size of the second resist layer
RL2 is obtained by using the second electron image having high
contrast, while the size of the hard mask layer HM is obtained by
using the reflective electron image having contrast.
As a result, the sample shown in FIG. 1F (which cannot be measured
by a conventional technique) can be measured with a reproducible
error of 0.5 nm. In addition, since the processed layer TL is not
etched in the state shown in FIG. 1F, it is easy to reproduce the
sample by re-performing the manufacturing process from the exposure
process.
(Fifth Embodiment)
FIG. 8 is a flowchart showing a measurement according to a fifth
embodiment of the present invention. After patterns are classified
into groups, a relative positional relationship between the groups
is detected in step 801. This is different from the other
embodiments. The relative positional relationship between the
groups means the amount of a superposition error between a pattern
subjected to an exposure and a pattern subjected to another
exposure. More specifically, the relative positional relationship
(positional error) in an X direction is obtained by using the
center of the contour (extending in a Y direction) of the pattern
as a reference, while the relative positional relationship
(positional error) in a Y direction is obtained by using the center
of the contour (extending in an X direction) of the pattern as a
reference. The superposition error between the pattern subjected to
the exposure and pattern subjected to the other exposure is very
important in order to measure the length of a space between the
pattern portions, and the size of a portion of the pattern
subjected to a multi-exposure. Since this method is not carried out
in conventional techniques, it is necessary that the apparatus
automatically classify the patterns into groups.
In the present embodiment, after the patterns are classified based
on the brightness, and the contour of each pattern is obtained, the
superposition error is obtained. When the superposition error is
large, the exposure process is re-performed. This contributes to
improvement in the yield of semiconductors.
In the embodiments of the present invention, a scanning electron
microscope using an electron beam is described as an example. The
basic concept of the present invention is not limited to this.
Another microscope using a charged particle beam such as an ion
beam can be applied to the present invention.
According to the present invention, it is possible to measure, with
high accuracy, the sizes of portions (having shapes different from
each other in a vertical direction) of a pattern on a sample
subjected to a multi-exposure and a relative positional
relationship between groups. Furthermore, it is possible to
smoothly control a lithographic process and an etching process.
* * * * *
References